Decking Calculator - Estimate Boards, Joists & Materials
Accurately calculate all materials for your deck project: decking boards, joists, bearers, stumps, and screws. Get instant estimates with wastage included.
Project Inputs
Spacing & Support
Use 0 to skip detailed post counts or when the deck is ledgered to a structure.
Deck Area Overview
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Deck area
Deck Area
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Decking (w/ waste)
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Joists
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Bearers
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Stumps / Posts
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Decking Screws
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Boards
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How to Use This Calculator
Enter your deck's footprint (length and width) and define the board profile plus spacing. Switch between Imperial and Metric units as needed and add a wastage percentage that accounts for offcuts and mistakes.
- Record the total deck length and width, keeping the values in the chosen unit system.
- Provide the decking board width plus the gap you will maintain between planks to calculate board count.
- Set the joist, bearer, and post spacing to estimate substructure length and counts.
- Add a waste allowance (10-15% is common) so linear footage covers cutting losses.
- Review the results and toggle the material summary table for a printable list of components.
Methodology
The calculator converts every dimension to inches, computes the number of boards and joists using evenly spaced centers, then converts back to linear units for you. Stump/post counts are derived by spacing along each bearer line, while screws are estimated as two per board-to-joist intersection. Wastage is applied to decking material at the final stage.
- Boards run across the deck width while joists are assumed to span the full width.
- Bearers run parallel to the deck width and support the joists; their count includes an extra member to finish the span.
- Results are shown in the chosen unit system, with easy toggles to switch between feet and meters.
Full original guide (expanded)
This section retains the verified references that accompanied the legacy calculator so nothing is lost during the refactor.